Studies on the relationship between protein conformation and enzymic activity are to be continued. Most specifically, we are interested in the changes in conformation and intramolecular interactions accompanying the transformation of pepsinogen to pepsin. These changes produce an enormous increase in enzymic activity and in the relative stability of the molecules. BIBLIOGRAPHIC REFERENCE: McPhie, P.: A turbidimetric milk clotting assay for pepsin. Anal. Biochem. 73: 258-261, 1977.